The present invention relates to an original feeding apparatus and an image reading apparatus provided with the original feeding apparatus. The image reading apparatus of the invention can be used for a device such as a copier, printer, facsimile machine or scanner.
An original feeding apparatus feeds an original or sheet stacked on an original feeding tray (original tray) one at a time to an original reading unit to read an image on the original. After the original reading unit reads the original, the original is discharged to a discharge tray.
In recent years, there has been increased a demand for an automatic document feeding apparatus with high quality reading performance. In such an automatic document feeding apparatus, a transport roller for transporting the original is required to transport the original linearly (without bending) relative to a transport direction without any variation. The demand for such transport performance has been increased in proportion to image quality.
FIGS. 7(A) to 7(C) are sectional views of a conventional original feeding apparatus with a large roller 131 (transport roller). Arrows shown in FIGS. 7(A) to 7(C) indicate positions on the original where the large roller 131 nips the original (position where an outer circumference of the large roller 131 contacts the original). As shown in FIGS. 7(A) to 7(C), in the conventional apparatus, the large roller 131 nips the original at various positions, at which the large roller 131 starts transporting the original. The conventional original feeding apparatus does not control the roller to contact the original at a constant position on the outer circumference thereof for reading the original.
FIG. 7(A) shows a nipping position of the large roller 131 on the original when nipping a first original. FIG. 7(B) shows a nipping position of the large roller 131 on the original when nipping a second original. FIG. 7(C) shows the nipping position of the large roller 131 on the original when nipping a third original. The nipping positions (contact positions of the outer circumference) of the large roller 131 for the respective originals vary and are inconsistent. Depending on when the large roller 131 starts rotating, the outer circumference of the large roller 131 contacts the original at a different position.
When a plurality of the originals is read consecutively, it is necessary to reduce variation due to eccentricity of the roller and to transport the originals in a constant manner (such as a constant transport speed and a constant feed amount). To this end, it has been tried to minimize the variation of the roller associated with rotation to improve precision of the transport roller. Specifically, it has been tried to improve circularity of the transport roller and the roller shaft, or prevent vibration of the roller caused by the rotation to increase the precision.
In the conventional original feeding apparatus described above, the large roller does not nip the original at a constant position (position of contact on the outer circumference) when the large roller starts transporting the original. In this case, when the roller does not have sufficient precision, the following problems may occur as the roller contacts the originals at different positions. For example, the original may be transported at a different speed. When one side of the roller has a transporting force different from that on the other side thereof in a direction perpendicular to the transport direction, it is possible to cause a variation in image alignment (such as a leading edge position, a side position and skew) for each original. Therefore, it is necessary to use a part with high precision to reduce the variation.
In order to improve the precision of the transport roller, it is necessary to implement advanced technology in a manufacturing process and quality control. For example, it may be necessary to add a process of polishing the outer surface of the roller after a process of molding the outer surface of the roller. The additional process increases the amount of work, thereby reducing the productivity of the part, increasing difficulty in the quality control, and increasing a cost of the part. Also, it is difficult to control the quality of a large quantity when the part has high precision.
In view of the problems described above, the present invention has been made, and the first object of the present invention is to provide an original feeding apparatus and an image reading apparatus in which an original is transported and read stably without using a part with high precision to reduce a variation when a plurality of the originals is processed continuously.
The second object of the present invention is to provide an original feeding apparatus and an image reading apparatus in which an operator can select a high quality mode for producing a high quality image and a non-high quality mode for reading the original at a high speed.
Further objects and advantages of the invention will be apparent from the following description of the invention.